This project addresses vascular heterogeneity within the liver and heart. We will examine how these specialized vascular beds respond differently to ubiquitous environmental signals, such as fluxes in extracellular nucleotides under both physiological and pathological states. Endothelial cells (EC) and vascular accessory cells differentially express ectonucleotidases of the CD39 family (e.g. NTPDase1/CD39, CD39L(ike)1/NTPDase2 etc.) that catalyze extracellular nucleotides. CD39/NTPDase1 can be shown to form a functional macromolecular complex with certain type-2 purinergic/pyrimidinergic receptors (e.g. P2Y2) and integrin receptors (e.g. alpha-v-beta3) on the endothelial surface; and also with a potential variety of intracellular downstream components (e.g. Ran Binding Protein M; RanBPM). We have shown that perturbations in levels of NTPDases have profound vascular-bed specific pathophysiological effects e.g. alterations in vascular permeability and local procoagulant responses. Expression of CD39 (or CD39L1) by fenestrated hepatic sinusoidal EC or cerebral microvasculature is very low under basal conditions. In contrast, cardiac EC(and pericytes) typically exhibit high levels of NTPDases. Following liver, brain or cardiac vascular injury there is dramatic upregulation of vascular-associated NTPDases. This process is associated with "capillarization" of the hepatic sinusoids. Deletion of cd39 in mutant mice dramatically increases hepatosplanchnic vascular permeability that promotes hemorrhagic death following ischemia and reperfusion injury. Extensive hemorrhagic stroke is observed following carotid occlusion in cd39-deficient mice. Further, cd39-cardiac transplants undergo rejection more rapidly than control grafts when transplanted into wild type mice or into rats in vivo. Specific Aims: 1) Determine the specific topology of the macromolecular complex by mapping out the differential expression of NTPDases, P2Y2 and alpha-v-beta3 in the cardiac and hepatic microvasculatures (under basal and pathological conditions). 2) Examine functional interactions between components of the complex that correlate with the differential expression of NTPDases and phenotypic properties of the cardiac and hepatic vasculatures. 3) Evaluation of regulatory role of NTPDases in vivo models of hypoxemia and inflammatory injury to hepatic and cardiac vasculatures. These studies are the first to study vascular diversity at the level of a macromolecular complex (rather than a single protein or gene) and will provide new information regarding extracellular nucleotide-mediated signaling in the endothelium. Understanding the differential integration of nucleotide-mediated cellular activation in different vascular beds could provide insights into novel therapeutic strategies for cardiovascular disease, stroke and hepatic vascular disorders.